1. Field of the Invention
The present invention relates to a polyester resin composition using as one of its material components a monosaccharide or a polysaccharide having a hydroxyl group, and a carboxyl group or an ion-exchanged carboxyl group. The present invention also relates to a process for producing the same.
2. Description of the Related Art
Throughout the twentieth century, oil resources were limitlessly exploited and used as the source of plastics or energy. However, not only do the oil resources have a limited reserve, but used plastics, when burned, produce large amounts of carbon dioxide and are blamed for many environmental problems such as global warming. Furthermore, waste plastic materials hardly break down in the natural environment and have thus brought about serious environmental pollution.
To cope with these problems, much effort has been made to develop materials that, when discarded and left in the natural environment, are naturally degraded by microorganisms or other natural factors into harmless materials.
One example is a polyester material disclosed in Japanese Patent Laid-Open Publication No. Hei. 9-143253, which is produced through condensation-polymerization of a polysaccharide such as cellulose with a hydroxycarboxylic acid, aliphatic polyol, or aliphatic polybasic acid. This material is known to be used as a biodegradable, environmentally clean molding material. Although the polyester material is biodegradable and brings about no environmental pollution when left in the natural environment after use, it cannot be recycled and therefore must be discarded after use. For this reason, the polyester material is economically unfavorable.
On the other hand, various attempts have been made to recycle the waste plastic material: currently, products molded from polyethylene terephthalate (PET) are collected, melted, and then remolded into various molded products. However, the plastic made from the recycled materials generally has reduced strength, heat-resistance and moldability when compared to newly synthesized plastic. For this reason, applications of recycled plastics are limited to those in which poor physical properties do not lead to any practical problem. As a result, plastic recycling is still not prevalent enough.